The present invention relates to an optical focusing system which consists of two mirrors which are ellipsoids of revolution.
For visual indicators for aircraft and for projection systems in the case of simulators, there is a need for wideangle focusing systems with a large field of vision (&gt;.+-.12.5.degree.) and large relative aperture (&gt;1:2), with widely spaced entrance pupil.
For these fields of use, it has already been proposed to use focusing systems having a concave mirror. In the known systems, the unsatisfactory correction of coma and astigmatism is a disadvantage. The condition for the correction of astigmatism in the case of surfaces of revolution of the second degree is also known. When using a surface of revolution of the second degree, astigmatism is corrected when the entrance pupil is located at a mathematical focal point of this surface. A focusing system having two mirrors which are ellipsoids of revolution is described, for instance, in British Pat. No. 1,132,605. In this known focusing system, however, the deviation from the isoplanasie condition is not corrected.
The object of the present invention is to apply the known conditions for the correction of astigmatism and at the same time correct the deviation from the isoplanasie condition, to a focusing system of large field of view, large relative aperture, and widely spaced entrance pupil.